1. Field of the Invention
This invention relates to crushing apparatus for frangible or friable material and more particularly to crushing apparatus of the gyratory type.
2. Description of the Prior Art
Existing types of primary, secondary and tertiary crushers for reducing the size of frangible or friable solids include gyratory crushers. A typical gyratory crusher consists of an inner truncated cone which revolves about a central vertical axis of an outer conical chamber to define a tapered annular space between the chamber and the cone. The inner cone has a circular movement about the vertical axis of the chamber but does not generally rotate about its own axis of symmetry.
The movement is given to the inner cone by a cam arrangement driven from beneath the cone by an external motor and gear train. The gear train rotates a large eccentric assembly comprising the cam arrangement which causes the shaft on which the cone is mounted to revolve about the vertical axis of the chamber whereby the point of intersection between the vertical axis and the gyratory axis is above the inner cone. Consequently, gyration is almost entirely horizontal resulting in the size of the annular space between the inner cone and outer chamber being relatively small at one side of the inner cone and relatively large at the opposite side of the cone during gyration. This large variation in the gap of the annular space results in a relatively large variation in the size of material discharged from the crusher. Consequently, when a particular material size is required, it is usually necessary for up to 40% of the discharged material to be re-crushed in order to reduce the same to a satisfactory size. Such inefficiency results in the crusher being subject to prolonged use and consequently increases the propensity of the crusher to wear and breakdown.
Additionally, the components of the crusher used for driving the inner cone in a gyratory manner from below the crushing assembly are required to be of a complex and precise design which makes the replacement of such components a very expensive task not only in terms of component costs but also in down time by requiring specialised maintenance or repair personnel to attend to such matters.